The 2010 summer was a relatively calm one as far as transfers are concerned, especially when compared to the 2009 summer, where Real Madrid alone spent about 250 million.
It seems that most clubs have learnt from Real Madrid's mistakes: despite having spent ridiculously high amounts of money on Kaka and Cristiano Ronaldo (among others), Real Madrid still came short to Barcelona in La Liga, lost prematurely in the Champions League against Lyon and experienced a humiliating defeat at the hands of Alcorcón in the Copa Del Rey. 250 million spent and no trophies for Los Blancos.
After this debacle, Real Madrid, now with Mourinho at the helm, was more careful with their transfer moves this summer, and other clubs have followed their example. Other than Manchester City, all the top European clubs adopted logical criteria in the selection of players to sign, trying to strengthen their squads (as opposed to totally rebuilding).
Let's take a look at the moves which, in my opinion, are likely to have the biggest impact during the season: